Dense magnesia-spinellide parts with synthesized magnesium chromite

Abstract

'man, and V. M. Ust'yantsev UDC 666.762.453 Magnesium chromite (magnesia--chromite spinel) is the most chemically resistant compound in relation to molten iron~ilicate slags [i, 2]. Magnesium chromite is one of the basic components of the spinellide of chromite ore and is present in it in the form of a solid solution with other spinellides.The presence of impurities, particularly silicates, in chromite ore has a significant detrimental influence on the quality characteristics of the refractories obtained.Therefore, for the production of refractories with increased resistance the use of purer magnesia--chromite raw material is necessary.Such raw materials include chromite obtained by thermal decomposition of magnesium bichromate.The method of its production was developed by the Ukrainian Scientific-Research Institute for Chemistry [3].We have conducted investigations on the use of synthesized magnesium chromite for the production of magnesia--spinellide refractories.As the result of the fact that the corrosion failure of refractories by slags occurs primarily in the binder, magnesium chromite was introduced into the finely ground component of the charge.To improve sintering of the refractory compositions, titanium magnetite concentrate was added to the composition of the magnesium chromite.Kempirsaisk deposit chromite ore of 3-1 mm fraction and sintered periclase powder of 2-0 mm fraction were used as the granular materials.The chemical and grain-size compositions of the original materials are presented in Tables i, 2.Refractory mixtures containing magnesium chromite sinter with difficulty and therefore the main problem was searching for a method of compacting the refractories.The search for the optimum conditions for obtaining dense parts was made with the use of the methods of mathe matical experiment planning.The open porosity P in %, which must be minimized, was adopted as the parameter of optimization.The independent variables influencing the density of the refractory are: ~, wt. % of sintering addition relative to the basic mixture; x2, temperature of preliminary firing of the magnesium chromite, deg C; x~, firing temperature of the samples, deg C; x4, wt. % of magnesium chromite in the charge; and xs, wt. % of granular chromite ore in the charge.The area of determination was the following: xl = 0.7-1.7%; x2 ~ 700-1500~ x3 = 1650-1850~ x4 = 25-35%; xs = 15-25%.To attain the extreme area the method of steep ascent was used [4]~ In the area close to the assumed extreme the subarea for linear approximation of the function of response was selected.In this subarea there was accomplished a 1/4 replica of the full facto~al experiment 2 s with the generating relationships;The samples were pressed in the form of cylinders with a diameter of 36 mm and a height of 40 mm under a pressure of 150 MPa and fired in the tunnel kilns of Magnesite Combine.Three parallel tests were made at each point of the plan.The regression coefficients with the use of the full factoral experiment or fractional replicas of it are dete...

Experiment planning in investigations of the influence of composition on the properties of refractories

“…As a result of its application in the third experiment it was possible to obtain a value for the porosity of 13.6% which in two subsequent experiments hardly changed. The plan and the results of the experiments are given in [6]. After II experiments it was possible to reduce the porosity of the article from 20 to 13.6%, and to determine the optimum parameters for obtaining dense magnesia-spinel refractories with synthetic magnesium chromite.…”

“…The Box--Wilson method was used to obtain dense magnesia--spinel articles containing synthetic magnesium chromite [6]. The open porosity, whose minimum was being searched for, was used as the optimization parameter.…”